A reduction in a heart's cardiac output (i.e., the reduced ability of the heart to output oxygenated blood from the left side of the heart) may result from various abnormalities and diseases of the heart. This reduction in output may be due, for example, to aortic valve disease. There are two major categories of aortic heart valve disease: stenosis and regurgitation. Stenosis involves the narrowing of the aortic outflow tract, causing obstruction to blood flowing from the left ventricle into the ascending aorta. The stenosis typically involves the buildup of calcified material on the valve leaflets, causing them to thicken and impairing their ability to fully open to permit adequate forward blood flow. Stenotic build up may also occur beneath the valve leaflets (i.e., subvalvular stenosis). Severe calcification can greatly impair proper functioning of the aortic valve and obstruct blood outflow from the heart. Regurgitation, on the other hand, is the retrograde leakage of blood back through the heart valve and into the left ventricle during diastole. Both stenosis and regurgitation of the aortic valve lead to left ventricular hypertrophy to compensate for the valvular dysfunction. Ultimately, there is dilatation and failure of the left ventricle resulting in decrease cardiac output and increased filling pressure in the heart.
Surgical treatments are available to treat valve dysfunction; however, these treatments have drawbacks. For example, the most common treatment for stenotic aortic valves is the surgical replacement of the diseased valve, which can be very invasive, requiring dissection of the patient's aorta. A particular drawback of conventional aortic valve replacement procedures is that they require the patient to be placed on the heart-lung machine (“on-pump”), wherein the heart is stopped and the surgery is performed through the patient's open chest. Because the success of these procedures can only be determined when the heart is beating, the heart must be closed up and the patient taken off the heart-lung machine (“off-pump”) before verification of surgical success can be made. If the off-pump results are determined to be inadequate, the patient must be put back on-pump and the aorta must be reopened. Moreover, the risks and complications associated with open-heart surgery—involving the use of cardiopulmonary bypass, aortic cross-clamping, and cardioplegic arrest—are well-known. The most serious risks of cardiopulmonary bypass and aortic cross-clamping are the increase in the likelihood of bleeding and stroke. Also, patients who undergo surgeries using cardiopulmonary bypass often require extended hospital stays and experience lengthy recoveries. Thus, while certain conventional heart surgeries produce beneficial results for many patients, numerous others who might benefit from such surgery are unable or unwilling to undergo the trauma and risks of conventional procedures.
Within recent years, minimally invasive types of procedures for coronary artery bypass surgery have been developed which do not require stopping the patient's heart and the use of cardiopulmonary bypass. While attempts have been made to treat aortic valves off-pump via endovascular procedures, such as endovascular balloon valvuloplasty, such procedures may provide only partial and temporary relief for a patient with a stenotic valve. Moreover, the rapid restenosis and high mortality following balloon aortic valvuloplasty have led to disfavor of this procedure in the field.
Even off-pump minimally invasive procedures currently used, such as endovascular aortic valve replacement, may include a risk of dislodgement of stenotic particles from the native aortic valve. Dislodged particles, or other debris released into the patient's cardiovascular system during surgery may travel to other parts of the patient's body and lead to obstructions and even strokes. Further, the delivery sheath requirement for the endovascular valves is large and many patients have peripheral vascular disease that precludes them from having this procedure. Therefore, a surgeon may desire to supplement blood flow through the patient's aortic valve without disturbing stenoses or other potentially obstructing material within the heart.